Refining hydrocarbon oil vapors with alkali and high boiling naphthenic acids



Dec. 11, 1956 C C. KLINE ETAL AND HIGH BOILING NAPHTHENIC'ACIDS Filed Dec. 8, 1954 Distillate Oils 5 Caustic Alkali l6 Caustic Treating l9 Secfion l8 Oil,AlkoliMelul OH comoimng l7 Nuphlhenaie's Alkall Napmhenic Acids 7 Mei'al Hydroxide Residue 22 Dlluem Exiroc'lion s w m v 33 Dlluem Dill-18117 Removal Acid Acidification Solveni Solvent Removal 3l 29 30 9 Distillation Acids Heavy Nophthenic Acids INVENTORS.

CHARLES C. KLINE HUGH L. MYERS Q. Mk

ATTO NE Y REFINING HYDROCARBON OIL VAPORS WITH ALKALI AND HIGH BOILING NAPHTHENIC ACIDS Charles C. Kline, Wallingford, and Hugh L. Myers,

Springfield, Pa., assignors to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Application December 8, 1954, Serial No. 473,957

3 Claims. (Cl. 196-36) This invention relates to the refining of hydrocarbon oil by contact thereof in vapor phase with an alkaline treating agent in liquid phase comprising alkali metal hydroxide, and more particularly to a method of cleaning a refining zone wherein such refining has been carried out.

It is known in the art to refine hydrocarbon oil by contact of the oil in vaporized condition with a liquid alkaline treating agent comprising alkali metal hydroxide. For example it is known to remove naphthenic acids and other acidic materials from hydrocarbon oil by such a process wherein the vaporized oil containing acidic material is passed upwardly through a distillation tower containing refining trays on which the liquid material is the alkaline treating agent. The latter flows downwardly in the distillation tower from one tray to the next lower tray and is removed from the tower at the lower end of the refining section of the tower. The acidic materials in the vaporized oil react with the alkaline treating agent to form for example alkali metal naphthenates which enter the liquid alkaline treating agent.

A difiicult problem which has been encountered in prior art operation involves the formation of carbonaceous deposits in the refining zone of the distillation tower. There is a tendency for these deposits to build up until they ultimately impair the efficiency of the operation or even require a shutdown of the apparatus. The nature of these carbonaceous deposits is not definitely known, but it is believed that they comprise in part carbonaceous materials formed by decomposition of constituents of the alkaline treating agent, such as alkali metal naphthenates or liquid oil which has been condensed from the oil vapors during the passage of the latter through the refining zone.

According to the present invention, a manner of removing carbonaceous deposits from the refining zone is provided. A particular advantage of the method of the present invention resides in the fact that it can be performed without shutting down the apparatus. The method of the invention involves passing a liquid cleaning agent comprising naphthenic acids through the renited States Patent 3O:-

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' cleaning action involves in part the neutralization of the alkaline materials in the carbonaceous deposits by the free naphthenic acids contained in the modified treating agent, since it has been found that a modified treating agent which has been used according to the method of the invention contains additional alkali metal naphthenates which apparently were formed during the cleaning operation.

The invention will be further described with reference to the attached drawing which is a flow sheet of a process for treatment of the oil vapors with an alkaline treating agent in a distillation tower, with solvent extraction to recover naphthenic acids from the alkaline treating agent, and with use of the naphthenic acids thus recovered to periodically acidify the alkaline treating agent in accordance with the method of the invention.

The drawing shows a distillation tower 10, a solvent extraction zone 11, solvent removal zones 12 and 14, acidification zone 13, and distillation zone 34). In operation hydrocarbon oil containing naphthenic acids is introduced into distillation tower 10 through line 15, and oil vapors containing naphthenic acids pass upwardly into the caustic treating section of the distillation tower. Liquid alkaline treating agent is introduced through line 16 onto the top tray of the caustic treating section. The alkaline treating agent passes downwardly through the caustic treating section and is removed from the lowest tray of the caustic treating section through line 17. During contact of the oil vapors with the treating agent in the caustic treating section, naphthenic acids react with alkali metal hydroxide in the treating agent to form alkali metal naphthenate in the treating agent, and also a portion of the oil vapors are condensed and become incorporated in the alkaline treating agent. The treating agent withdrawn through line 17 preferably contains about 60% to oil, and more preferably at least about 86% oil.

All or a part of the withdrawn alkaline treating agent can be withdrawn from the system through line 18. However a preferred operation involves recycling a portion of the withdrawn treating agent through line'19 into the upper part of the caustic treating section, and passing the remainder of the withdrawn treating agent as a drag stream through line 20 into extraction zone 11. A

selective solvent for alkali metal naphthenates and alkali metal hydroxide, e. g. aqueous isopropanol, is introduced into extraction zone 11 through line 21. A diluent solvent for hydrocarbon oil, e. g. petroluem naphtha, is introduced into extraction zone 11 through line 22. Solvent containing dissolved alkali metal naphthenates and alkali metal hydroxide is withdrawn through line 23 into acidification zone 13. Diluent containing dissolved hydrocarbon oil is withdrawn from extraction zone 11 through line 24.

In diluent removal zone 12, the diluent is stripped from the hydrocarbon oil, and the recovered oil is removed through line 25 and recycled entirely or in part through lines 26 and 33 into the caustic treating section. The purpose of such recycling is to maintain a high oil content in the alkaline treating agent, since such high oil content reduces the formation of objectionable carbonaceous materials through decomposition of constituents of the alkaline material.

An acid, e. g. concentrated sulfuric acid, is introduced into acidification zone 13 through line 28. and reacts with alkali metal naphthenates to form free naphthenic acids. The latter are separated in solvent removal zone 14 from the aqueous phase of the acidification products and are withdrawn through line 29. The naphthenic acids are distilled in zone 30 to obtain a withdrawn through line 34.

During the ordinary operation of the distillation tower, all of the naphthenic acids thus recovered are Withdrawn through line 35. During the cleaning period,

on the other hand, all or a portion of the naphthenicacids is passed through lines 31 and 33 into the caustic treating section, the passage of oil through line 33 into the treating agent preferably being reduced in rate or discontinued. The amount of naphthenic acids introduced is sufiicient to neutralize the excess alkalinity of the treating agent and to provide free naphthenic acids in the upper part of the treating section. The acids can if desired be introduced into the treating agent prior to introduction of the latter into the caustic treating section.

During the ordinary operation of the distillation tower fresh alkali metal hydroxide, e. g. aqueous or molten caustic soda or potash or mixtures thereof, is introduced periodically or continuously into the caustic treating section through lines 32 and 16, in order to maintain the alkalinity of the treating agent at the desired level. During the cleaning operation however such introduction is preferably discontinued.

The modified treating agent is passed downwardly through the caustic treating section during the cleaning operation in the same general manner that the alkaline treating agent is passed therethrough during ordinary operation. During the cleaning operation carbonaceous deposits which accumulated on the metal surfaces of the caustic treating section during the previous ordinary operation are removed from the caustic treating section. At the termination of the cleaning operation, the supply of naphthenic acids to the treating agent through line 31 is discontinued, and the introduction of alkali metal hydroxide into the treating agent through line 32 is resumed or increased in order to restore the alkaline condition of the treating agent, and the ordinary operation of the distillation tower is resumed.

It is not necessary according to the invention to employ naphthenic acids recovered from the same process system, as the means for acidifying the treating agent preparatory to the cleaning operation. Instead, naphthenic acids obtained from some extraneous source can be employed.

' The following example illustrates the invention:

An operation similar to that illustrated in the drawing was carried out, employing a reduced naphthenic crude as charge stock. Liquid alkaline material containing about 8284 percent oil, the remainder being mainly alkali metal naphthenate with a small amount of alkali metal hydroxide, was removed through line 17 at a rate of about 110 volumes per hour, about 100 volumes per hour then being passed through line 19 and about volumes per hour through line 20. -Oil recovered by extraction was passed through lines26 and 33 at a rate of about 7 volumes per hour.

This operation was continued for a period of about days, during which time there was a gradual increase in the pressure drop across the caustic treating section, indicating that deposits were accumulating in the section and causing greater resistance'to vapor flow. At the end of the 20-day period, pressure drop had risen to 33 mm. Hg.

The introduction of caustic through line 32 and the passage of oil through line 33 were then discontinued, and the introduction of naphthenic acids through lines 31 and 33 into the treating agent was begun, and continued for a 24 hour period, at a rate of about 4 volumes heavy distillate which is' per hour. The naphthenic acids used had acid number of about 127 mg. of KOH per gram.

At the end of the 24 hour treatment, the normal operation was resumed, i. e. the addition of naphthenic acids was ceased, and the addition of oil and caustic begun. again. The treatment was found to have been highly effective. No pressure drop reading was, made at the end of the treatment, but twelve hours thereafter the pressure drop was found to be 19 mm. Hg. indicating, by comparison with 33 mm. Hg. prior to the treatment, that the obstructive deposits had been largely removed.

During the 24 hour treatment, the viscosity of the material removed through line 17 greatly increased. The content of alkali metal naphthenates in the material remained substantially constant during the treatment; this indicated that alkaline material contained in deposits had reactedwith naphthenic acids, since no alkaline. material was added from any other source during the treatment, and the naphthenate content of the material would have decreased by bleeding through line 20 if additional naphthenic acids had not reacted with alkaline material.

This example shows that the refining zone of a vapor weight of the naphthenic acids contained in "the oil vapors rising through the refining zone.

The liquid cleaning agent produced by adding naphi thenic acids to the alkaline treating agent preferably con-;

tains only a minor amount of free naphthenic acids, e. g., 0.1 to 10 volume percent. In the example given, the remainder of the cleaning agent comprised essentially alkali metal naphthenates and oil, the supply of the latter to the cleaning agent during the treatment being maintained by condensation of oil in the caustic treating section and by condensation of oil in the higher portions of the tower with reflux on the caustic treating section. However, the source of the other constituents of the cleaning agent is not essential to the invention, as long as they provide a suitable liquid carrier for the naphthenic acids.

The temperature of the cleaning operation will generally be in the approximate range from 500 F. to 700 F. In preferred operation, the cleaning operation is performed under the same general conditions, including temperature, as the ordinary refining operation.

During the ordinary refining operation, the material withdrawn from the caustic treating section through line 17 generally contains alkali metal hydroxide, as indicated in the drawing. During the cleaning operation, on the other hand, thematerial withdrawn through line 17 preferably does not contain any substantial amount of alkali metal hydroxide, excess alkali metal hydroxide having been neutralized by addition of naphthenic acids. Preferably, the material withdrawn through line 17 during the cleaning operation does not contain any substantial amount of naphthenic acids, the acids introduced through A line 33 having been largely neutralized during passage through the caustic treating section by alkaline materials therein.

The invention claimed is: a

1. Method for refining petroleum which comprises: contacting petroleum vapors with a liquid treating agent comprising alkali metal hydroxide in a refining zone, thereby to react naphthenic acids contained in said vapors with said hydroxide; periodically introducing free naphthenic acids in liquid phase into said refining zone, which acids have average molecular weight higher than that or the first-named naphthenic acids, thereby to effect a cleaning of said refining zone by means of the latter naph thenic acids.

2. Method according to claim 1 wherein during a first period said liquid treating agent containing oil, alkali 5 metal naphthenates, and alkali metal hydroxide, is circulated through said refining zone, with addition of alkali metal hydroxide to said treating agent to maintain alkalinity, wherein naphthenic acids are recovered from a drag 1,784,262 stream removed from the circulating treating agent, and 10 2,658,027 wherein during a second period, addition of alkali metal hydroxide to said treating agent is ceased and the recovered naphthenic acids are added to said treating agent.

3. Method according to claim 1 wherein said petroleum vapors are lubricating oil vapors.

References Cited in the file of this patent UNITED STATES PATENTS Wheeler Dec. 9, 1930 Hoover NOV. 3, 1953 

1. METHOD FOR REFINING PETROLEUM WHICH COMPRIES: CONTACTING PETROLEUM VAPORS WITH A LIQUID TREATING AGENT COMPRISING ALKALI METAL HYDROXIDE IN A REFINING ZONE, THEREBY TO REACT NAPHTHENIC ACIDS CONTAINED IN SAID VAPORS WITH SAID HYDROXIDE; PERIODICALLY INTRODUCING FREE NAPHTHENIC ACIDS IN LIQUID PHASE INTO SAID REFINING ZONE, WHICH 